At the end of last week Sony Mobile started pushing out Android 4.1.2 upgrades to Xperia T owners living in Europe and this week Japan-based OEM seems to have started spreading JellyBean firmware build 9.1.A.0.490 to Xperia V, according to user reports.
The upgrade apparently rolls in Northern and Eastern Europe and in Singapore. Sony hasn’t confirmed anything through official channels.
You can try to check if the new build is available in your area by going into Settings > About phone > Software updates > Check for updates or through Sony PC companion software. There is another alternative if you do have custom ROM flashing experience.
These stock ROMs have been shared on XDA forums by users who already got the upgrade.